Resistance 2 was particularly shit for me. Just didn't capture the atmosphere of the original. Resistance 3 is brilliant though and a welcome return to form.

Gears 2 was also underwhelming. It was too dark most of the time and and the broken online killed it for me.

Tekken 6 was shite because they turned it into an utter n00bish juggle fest. Never buying a future Tekken game again if they intend to stick with the crap gameplay.

Halo 3 for me is the worst of the series campaign wise. Online was good as expected, but Bungie really dropped the ball with the level design this time. I distinctly remember finishing the campaign mode on hard difficulty in just over 5 hours. That's never good for any kind of game.

Bioshock 2 was an ok game but completely pointless. I was so psyched for it after the utterly superb original, but it ended up being too samey and boring in the end.

Oblivion, Fallout and StarCraft 2 would all have been ok games if they hadn't been sequels, but comparing them to the originals leaves them severely lacking.

Witcher 2 and Mass Effect 2 are just bad though, even if I don't consider the originals.

A few more sequels:
Breath of Fire 5
Might & Magic 8-9
Every Sims game, ever (because the original architect concept was far more interesting, but was replaced by a people simulator)
GTA4
Unreal Tournament 3

Dragon Age 2, by the time I'd got to the end. I thought it started quite promising but it all went wrong...

Purely on a technical level I'd say Halo 3.

Resistance 2 for losing the split screen campaign and weapon wheel.

Every FF since FF9 for losing the overworld map and concentrating on badly voiced cut scenes. I'd probably omit FFXII from that list as it was at least trying something different and I remember really enjoying once I got over the fact that there was bugger all story and character interaction.

Far Cry 2: massive disappointment after the sublime Far Cry by Crytek. That one is still their best game!Assassin's Creed II: yes it was better than 1 but not by much. Still a crap game with a lot of wasted potential. Unreal Tournament 3: Had it's moments, but missed wat the previous games made special. Also not the best show of the UE 3. Oblivion: a much, much worse game compared to it's excellent predecessor on almost every level.Dawn of War 2: Not a bad game by any means, but far from as great as the first. Star Wars: Knights of the Old Republic 2: buggy, unfinished, lots of wasted potential.

I would add Dragon Age 2 (obviously), but I haven't played any game in the series. Can't get myself past the awful, boring art style. Would not be so much of an issue if the graphics didn't suck on a technical level too.

Oblivion, Fallout and StarCraft 2 would all have been ok games if they hadn't been sequels, but comparing them to the originals leaves them severely lacking.

Witcher 2 and Mass Effect 2 are just bad though, even if I don't consider the originals.

A few more sequels:
Breath of Fire 5
Might & Magic 8-9
Every Sims game, ever (because the original architect concept was far more interesting, but was replaced by a people simulator)
GTA4
Unreal Tournament 3

Ah, so we've just progressed to a random list of ( actually mostly pretty good sequels ) and the critical analysis of "they are shit". Brilliant.

Crackdown was fantasic and great fun from start to end. Crackdown 2 was so bad that i gave up after just a few hours.

Shame as i really wanted Crackdown 2.

Spot on. I want morphing cars fo fook sake. Loved the first game, 2nd was toss. I also "completed it" in a couple of hours, due to joining someone at random I must point out, who was on the last boss/battle thing, cue end credits!

On Topic:

Resident Evil 4 and 5: played and completed and enjoyed both, however not what I really wanted.
Saw II (just too many qte's this time)
Fable III: I enjoyed a lot but again not as good as II
All the Drivers post 1 until the sublime SF
FEAR 2